Problem: $ F = \left[\begin{array}{rrr}2 & 0 & 1 \\ 4 & -1 & 4 \\ 4 & -2 & 2 \\ 1 & -1 & 2\end{array}\right]$ What are the dimensions of matrix $ F$ ?
Explanation: The first dimension is the number of rows in the matrix. How many rows does $ F$ have? The second dimension is the number of columns in the matrix. How many columns does $ F$ have? So, $ F$ is a 4 $\times$ 3 matrix.